Field of the Invention
The invention relates to a push pull type control cable which is improved to impart a good operability with an added comfortability.
In a push pull type control cable which connects a shift lever to a vehicular transmission, a wire is provided by winding a side wire around a core wire, and arranged to be axially movably placed within a liner. A zinc plating treatment is provided on an outer surface of the side wire to impart a rust resistant property and facilitate a mobility at once between the wire and the liner.
On the other hand, the side wire forms a multitude of steel lines wound around the core wire at a predetermined lead angle.
However, an endurance of the zinc plating treatment has not been satisfactorily considered, and its thickness dimension has been 1.0.about.3.0 .mu.m. With the passage of service time, it is feared that the zinc plating separates partly from the side wire due to the friction against the liner so as to increase a coefficent of friction. The increased coefficent of friction reduces a load efficiency which represents a ratio of an output load to input load so as to eventually reduce the operability and sensible quality. This resultantly requires the replacement of the control cable itself.
In the meanwhile, a relationship between the lead angle and the load efficiency has not seriously been taken into account. In order only to prevent the side wire from getting loose, the lead angle has been determined to be 25.about.30 degrees. With the increase of the lead angle, it is found that a contact area between the side wire and the liner increases to add a further frictional resistance therebetween so as to reduce the load efficiency. Once the contact area has increased, a frictional surface of the liner predominantly wears to increase the contact area acceleratively so as to significantly reduce the load efficiency with an added frictional resistance.
The reduced load efficiency requires an added operable force to deteriorate the sensible quality with decreased endurance. In recent years, it has been demanded to ameliorate the sensible quality, and at the same time, enabling consumers to a maintenance free period long enough to reach a product life span in the field of durable consumer goods such as a motor vehicle.
Therefore, the present invention has made with the above drawbacks in mind, it is a main object of the invention to provide a push pull type control cable which enables consumers to an extended maintenance free period with a high load efficiency and sensible quality.